CES Blast Effects & Damage Assessment 2 — Questions and Answers
Question 1: What is the term for the secondary phase of a blast wave where air pressure drops below ambient atmospheric pressure?
- Negative phase (Correct answer)
- Mach stem
- Rarefaction front
- Subsonic tail
Correct answer: Negative phase
The negative phase (suction phase) follows the positive phase and can cause structures to be pulled outward after the initial push.
Question 2: Which factor MOST significantly increases the scaled distance when assessing blast damage potential?
- Increased charge weight
- Decreased standoff distance
- Increased standoff distance (Correct answer)
- Higher detonation velocity
Correct answer: Increased standoff distance
Scaled distance (Z = R / W^(1/3)) increases as standoff distance R increases, indicating lower blast damage potential.
Question 3: A structure experiencing 'progressive collapse' after a blast has failed primarily due to which mechanism?
- Thermal weakening of steel
- Loss of load-bearing columns removing support for upper floors (Correct answer)
- Glass fragmentation cutting structural ties
- Soil liquefaction undermining the foundation
Correct answer: Loss of load-bearing columns removing support for upper floors
Progressive collapse occurs when the loss of key load-bearing members causes successive floor failures in a chain reaction.
Question 4: In the context of explosion injuries, which organ system is MOST vulnerable to primary blast injury?
- Musculoskeletal system
- Central nervous system
- Air-containing organs (lungs, GI tract, ears) (Correct answer)
- Circulatory system
Correct answer: Air-containing organs (lungs, GI tract, ears)
Primary blast injury results from the pressure wave acting on gas-filled organs, with the lungs and eardrums being most susceptible.
Question 5: What does the 'impulse' of a blast wave measure?
- Peak overpressure at a point
- The speed of the shock front
- The area under the pressure-time curve (Correct answer)
- Distance from the detonation point
Correct answer: The area under the pressure-time curve
Impulse is the integral of overpressure over time and determines the total force imparted to a structure or body.
Question 6: When a blast wave travels from soil into an above-ground structure, the transmitted pressure is affected by:
- The color and reflectivity of the structure's surface
- Impedance mismatch between the soil and structural material (Correct answer)
- The ambient temperature at the time of detonation
- The explosive's oxygen balance
Correct answer: Impedance mismatch between the soil and structural material
Impedance mismatch between media governs how much blast energy is transmitted, reflected, or absorbed at an interface.
Question 7: Which window glass condition provides the GREATEST fragmentation hazard at a given standoff distance?
- Tempered glass with safety film
- Annealed glass without any film (Correct answer)
- Laminated safety glass
- Polycarbonate panels
Correct answer: Annealed glass without any film
Annealed (ordinary) glass without film shatters into large, sharp fragments that travel at high velocity and cause severe laceration injuries.
CES Blast Effects & Damage Assessment 2
What is the term for the secondary phase of a blast wave where air pressure drops below ambient atmospheric pressure?